Contactless direct current motor reversing circuit

ABSTRACT

A contactless, reversing circuit for a direct current motor, wherein the current from a variable frequency pulsed, direct current source is applied to the series field of the motor by a first pair of solid state switching devices for forward rotation of the motor, and by a second pair of solid state devices for reverse rotation of the motor. An additional single solid state switching device, common to both pairs of devices and normally carrying the induced armature current during a blocking period between pulses, is de-energized during the transfer of conduction between the one direction pair to the other direction pair of devices, in order to assure the blocking state of the one pair before the other pair is turned on.

United States Patent Van Der Linde et al.

[54] CONTACTLESS DIRECT CURRENT MOTOR REVERSING CIRCUIT [72] Inventors:John R. Van Der Linde, Salem; Lyle W. Fairey, Roanoke, both of Va.

[73] Assignee: General Electric Company [22] Filed: Sept. 28, 1970 [21]App]. No.: 75,853

[52] U.S. Cl ..318/139, 318/300 [51 Int. Cl. ..H02r 5/16 [58] Field ofSearch ..318/246, 251, 293, 294, 300,

[ 1 Sept. 26, 1972 Frank L. Neuhauser, Oscar B. Waddell and Joseph B.Forman [5 7] ABSTRACT A contactless, reversingvcircuit for a directcurrent motor, wherein the current from a variable frequency pulsed,direct current source is applied to the series field of the motor by afirst pair of solid state switching devices for forward rotation of themotor, and by a second pair of solid state devices for reverse rotationof the motor. An additional single solid state switchingdevice, commonto both pairs of devices and normally carrying the induced armaturecurrent during a blocking period between pulses, is de-energized duringthe transfer of conduction between the one direction pair to the otherdirection pair of devices, in order to assure the blocking state of theone pair before the other pair is turned on.

5 Claims, 1 Drawing Figure F IELD IIIII. II

i'HYRISTOR CHOPPER- DIRECTION .5

swrrcH PAIENTEDsms um I I I INVENTORS JOHN R. VAN DER LINDE LYLE W.FAIREY BACKGROUND OF THE INVENTION In electric vehicles, such as batterytrucks and forklift trucks, a motor having a series field and operatedfrom a battery source is repeatedly reversed in the direction ofrotation. In the past this function has been performed by two or fourdirection contactors which are so connected to the series field of themotor that one set of contacts of the contactors will energize the fieldin one direction while the other set of contacts allows current to flowin the opposite direction through the series motor field.

In dust laden or corrosive atmospheres, contact life of these contactorsbecomes limited through chemical and abrasive action, resulting infaulty operation of the vehicle. In order to avoid this condition,maintenance at predetermined intervals is required. Contactors, as allother mechanical apparatus, are subject to wear, resulting in unreliableoperation and eventual replacement of the entire contactor.

In an explosive atmosphere, there exists the possibility that arcing ofthe contacts may cause fire and explo- SUMMARY OF THE INVENTION In orderto overcome these problems, the present invention provides a staticswitching circuit whereby the above-noted direction contactors arereplaced by two pairs of solid state switching devices, each pairconnected to the motor field in a manner which directs the currenttherethrough in a direction opposite of the other pair. Also included isan additional solid state switching device which normally conducts theflyback or armature-induced current during the blocking period of thedirection devices. .This additional device is connected in series withboth pairs of direction switching devices.

During change of direction of the motor, i.e., when conduction of thecurrent is transferred from one pair of switching devices to the other,the single switching device is de-energized in order to allow theconducting pair of direction devices to turn off before the opposingpair of direction devices is turned on.

BRIEF DESCRIPTION OF THE DRAWING The drawing illustrates a contactlessreversing circuit in accordance with a preferred embodiment of thepresent invention.

DETAILED DESCRIPTION In the ensuing description, the several solid stateswitching devices are termed thyristors. It is to be understood thatthese devices, while termed thyristors, may be any semiconductors orcombination of semiconductors which performs the switching functions ofa thyristor.

The combination of a PNP and a NPN transistor interconnected to formaregenerative feedback pair is an example of a possible substitution inperformance of the static latching switching functions of the thyristor.

Referring to the drawing, a positive terminal of storagebatteryllprovides electrical current to one side of a transformerprimary winding 13, the other side of which connects to the cathode ofthyristor l7 and to the anodes of a pair of direction thyristors 19 and21.

For motor rotation in one direction, current will pass through thyristor19, motor field 25, and through a thyristor 27 into motor armature 31;or when opposite rotation is required, current is conducted throughthyristor 21, motor field 25, and a thyristor 23 to motor armature 31. Adiode 29 is connected in parallel to ar- 0 mature 31 and opposes thenormal flow of electrical current through the direction circuit 26,which is made up of thyristors 19, 21, 23, and 27 and further includesmotor field 25. Diode 29 provides a conductive path for the inducedarmature current when the motor is reversed while rotating. The otherside of armature 31 connects to the anode of thyristor 17, and athyristor chopper circuit 33 (illustrated in block form) which providesa conductive path for the induced armature current when the motor isreversed while rotating. A connection from the thyristor chopper 33 tothe negative terminal of the storage battery 1 l completes thearmature-series field loop of the circuit.

Storage battery 11 also provides current to a common connection 63 of adirection switch 15. A contact 55, when closed, allows current to beconducted from common connection 63 through a diode 37, a resistor 35into the gate of direction thyristor 21, and through a diode 49 and aresistor 47 into the gate of direction thyristor 23.

Similarly, when contact 57 of switch 15 is closed, it allows currentfrom common connection 63 to be con ducted through a diode 45 and aresistor 43 into the ate of direction thyristor 27, as well as through adiode 41 and a resistor 39 into the gate of direction thyristor 19.Resistors 35, 39, 43, 47 and an additional resistor 51 are provided tolimit the current level input to the gates of he thyristors. Diodes 37,41, 45, 49 and a further diode 53 provide isolation whereby each of thethyristors is gated individually in order to avoid the simultaneousconduction of both the forward and reverse thyristors. The directiondesignations forward and reverse are arbitrarily assigned to contacts 55and 57, respectively. Thus when contact 55 is closed, current isconducted through the series motor field 25 in a direction whereby themotor armature 31 is caused to rotate in the forward direction.Similarly, when contact 57 is closed, current is conducted through theseries motor field 25 in a direction whereby the motor armature 31 iscaused to rotate in the reverse direction.

Two additional contacts, 59 and 61, are connected in parallel and directcurrent through diode 53 and resistor 51 into the gate of thyristor 17when direction switch 15 is in either the forward or reverse state. Bothcontacts 59 and 61 are, however, in nonconducting state during thetransfer of the switch 15 from one direction state to the other.

In prior art, contactors are used in the place of thyristors 19, 21, 23,and 27, the contacts of which allow current conduction of the seriesmotor field to be changed in direction in a similar manner as describedabove.

Reference is made to US. Pat. No. 3,344,328 titled Direct Current MotorPlugging Circuit by H. E. Morris for a complete description of motorreversing by means of contactor switching. The referenced patent alsocontains a full description of the operation of the thereby controllingthe rotational speed of the armature 31.

In the prior art, a diode is provided which carries current induced inthe motor armature during the off period of the thyristor choppercircuit; i.e., when no current is being conducted through the motorarmature from an outside source (the increment of time between adjacentpulses). This induced armature current is termed flyback current,resulting in the diode being termed the flyback diode. In the presentinvention, a thyristors 17 termed the .flyback thyristor, performs thefunction of circulating the flyback current in addition to otherfunctions which will be described later.

The characteristics of a thyristor are such that a momentary positivepulse applied to the gate thereof will cause the thyristor to conduct;however, in order to be turned off, it is necessary in addition toremoving the gate applied signal to either remove all power from thethyristor or to momentarily apply reverse voltage between the cathodeand anode thereof. Thus, during the on period of the thyristor choppercircuit 33, the potential across the thyristor 17 is such that thegreater positive value is applied to the cathode, causing this thyristor17 to turn off. However, during the off period of the thyristor choppercircuit 33, the induced current from the armature will circulate throughthyristor 17, providing a gate signal is present, and through one pairof thyristors of direction circuit 26.

As previously stated, thyristors 19 and 27 or 21 and 23 provide meansfor reversal of current flow through the motor field 25 depending onwhich of pairs of thyristors is energized. With the closing of contact55 of directional switch 15, corresponding to the forward direction,current will pass from the common connection 63 through contact 55through diodes 37 and 49 and resistors 35'and 47, respectively, tothyristors 21 and 23, thus placing these thyristors in a conductivestate. Current will be conducted through thyristor 21, through field 25in the direction from right to left and through thyristor 23 beforeflowing through armature 31. Conversely, contact 57 represents thereverse contact of direction switch and when closed allows current to beconducted from the common connection 63 through diodes 41 and 45 andresistors 39 and 43 to thyristors 19 and 27, respectively, therebyplacing these thyristors in a conductive state. Current passes throughthyristor 19 and motor field in the direction from left to right, andthyristor 27 to armature 31. With respect to armature 31, the directionof current is reversed through the field 25 from the previouslydescribed example. These currents are conducted only during the on timeof the thyristor chopper circuit 33. An induced current flowing throughthyristor 17 during the off period of the thyristor chopper circuit 33tends to maintain the preselected thyristors l9 and 27 or 21 and 23 ofthe direction circuit 26 in a conductive state. This condition producesa problem when reversal of the motor is required.

With one pair of thyristors in conducting state, a possibility exists ofa direct short-circuit when the opposing pair of thyristors isactivated. it is, therefore, necessary that one pair of thyristors benonconducting before the opposing pair is turned on. This condition isrealized by momentarily removing all power from the direction circuit26. Thyristor 17 performs the function of interrupting the circulatingflyback current during the off period of the chopper circuit 33, therebycausing all power to be removed from the thyristors in the directioncircuit 26, allowing the conducting pair of thyristors to turn offbefore the other pair of thyristors is turned on.

The gate signal is appliedto thyristor 17 by closing either of thecontacts 59 or 61 of direction switch 15 which is designed to providecontact opening of both these contacts during transfer from one contactto the other. For example, assume that the motor is rotating in theforward direction so that contacts 55 and 59 of the directional switch15 are closed. A current is, there fore, applied through contact 59,diode 53 and resistor 51 to the gate of thyristor 17, thereby placingthis thyristor in a conductive state. A current is also conductedthrough contact 55 and through associated diodes and resistors to thegates of thyristors 21 and 23. When reversal of the motor 31 is desired,the directional switch 15 is operated, opening contacts 55 and 59 andclosing contacts 57 and 61. Thus, during the operation of directionalswitch 15 from the forward position to the reverseposition, a period oftime exists during which all the contacts of the direction switch 15 areopen. This removes the gate signal from thyristors 17, 19, 21, 23, and27'. Thyristor 17 turns off and blocks the circulating current whichexists during the off time of thyristor chopper circuit 33. Current isthereby prevented from passing through thyristors 21 and 23 at thistime. This assures that these thyristors are also placed in anonconducting state. When contacts 57 and 59 close in the reverseposition of directional switch 15, power is supplied to the gates ofthyristors 19 and 27, allowing these thyristors to conduct current fromthe battery 11 to the motor. Simultaneously, contact 61 is closed andallows current to be applied to the gate of thyristors 17; so thatduring the off period of chopper circuit 33 the induced current from thearmature 31 circulates through thyristor l7 and the reverse thyristors19 and 27. Conversely, when the directional switch 15 is rotated to theforward position, contacts 57 and 61 now open before contacts 55 and 59close. the circulating current is blocked by nonconducting thyristor 17which causes thyristors 27 and 19 to turn off. When the gate current isnow conducted by contact 55, thyristors 21 and 23 are placed in aconductive state which allows current from the storage battery 11 to beapplied to the motor. When contact 59 closes, the gate signal is appliedto thyristor 17 which allows the induced current from the armature 31 tobe applied to the forward thyristors 21 and 23 and through series field25 to armature 31, thereby reversing the direction of the motor.

Thus, during a change of direction of the motor, a

nonconducting state of one pair of direction thyristors is assuredbefore the opposing direction pair of thyristors is placed in aconducting state.

While the invention has been explained and described with the aid ofparticular embodiments thereof, it will be understood that the inventionis not limited thereby and that many modifications retaining andutilizing the spirit thereof, without departing essentially therefrom,will occur to those skilled in the art in applying the invention tospecific operating environments'and conditions. It is thereforecontemplated by the appended claims to cover all such modifications asfall within the scope and spirit of the invention.

What is claimed is:

l. A contactless reversing circuit for controlling the direction ofrotation of a direct current motor, which is supplied from a pulseddirect current source, said motor having a field winding comprising:

a. first pair of solid state switching devices connected to the motorfield winding for directing current through the motor field winding inone direction;

. a second pair of solid state switching devices connected to the motorfield winding for directing current through the motor field winding inthe opposite direction;

0. first means for selectively providing gate signals to each pair ofswitching devices;

. a single solid state switching device connected in parallel with said,motor and common to both pairs of switching devices for interrupting thecurrent in the conducting pair of switching devices; and,

e. second means for selectively providing a gate signal to said singlesolid state switching device, said first and said second means beingoperatively associated to ensure that absent a gate signal to one ofsaid pairs of switching devices, no gate signal can be provided to saidsingle switching device.

2. The invention in claim 1 wherein said solid state switching devicesare thyristors.

3. The invention claimed in claim 2 wherein the single thyristor isde-energized during the transfer of current conduction from the firstpair of thyristors to the second pair of thyristors.

4. The invention claimed in claim 2 further including means forenergizing and de-energizing the gate of the single thyristorsimultaneously with the energization and de-energization of the gates ofeach of the pairs of thyristors.

5. A contactless reversing circuit for controlling the direction of adirect current motor which is supplied from a direct current source,said motor having a field winding, comprising:

a. a first pair of thyristors connected to the motor field winding fordirecting current through the motor field in one direction;

b. a second pair of thyristors connected to the motor field winding fordirecting current through the motor field winding in the oppositedirection;

0. a thyristor chopper circuit connected in series with said motor andsaid direct current source for producing a pulsed variable frequencydirect current;

d. a single thyristor connected in parallel with said motor and commonto said pairs of thyristors and connected to block current from thedirect current source, said single thyristors normally conductingcurrent generated by the motor during the interval between pulses; and

switching means for selectively supplying gate si alst each of said resectiye airs ofthyristors a d sa1 single thyristoi said switching meansserving to supply gate signals to said single thyristor only when gatesignals are supplied to one of said pairs of thyristors.

1. A contactless reversing circuit for controlling the direction ofrotation of a direct current motor, which is supplied from a pulseddirect current source, said motor having a field winding comprising: a.first pair of solid state switching devices connected to the motor fieldwinding for directing current through the motor field winding in onedirection; b. a second pair of solid state switching devices connectedto the motor field winding for directing current through the motor fieldwinding in the opposite direction; c. first means for selectivelyproviding gate signals to each pair of switching devices; d. a singlesolid state switching device connected in parallel with said motor andcommon to both pairs of switching devices for interrupting the currentin the conducting pair of switching devices; and, e. second means forselectively providing a gate signal to said single solid state switchingdevice, said first and said second mEans being operatively associated toensure that absent a gate signal to one of said pairs of switchingdevices, no gate signal can be provided to said single switching device.2. The invention in claim 1 wherein said solid state switching devicesare thyristors.
 3. The invention claimed in claim 2 wherein the singlethyristor is de-energized during the transfer of current conduction fromthe first pair of thyristors to the second pair of thyristors.
 4. Theinvention claimed in claim 2 further including means for energizing andde-energizing the gate of the single thyristor simultaneously with theenergization and de-energization of the gates of each of the pairs ofthyristors.
 5. A contactless reversing circuit for controlling thedirection of a direct current motor which is supplied from a directcurrent source, said motor having a field winding, comprising: a. afirst pair of thyristors connected to the motor field winding fordirecting current through the motor field in one direction; b. a secondpair of thyristors connected to the motor field winding for directingcurrent through the motor field winding in the opposite direction; c. athyristor chopper circuit connected in series with said motor and saiddirect current source for producing a pulsed variable frequency directcurrent; d. a single thyristor connected in parallel with said motor andcommon to said pairs of thyristors and connected to block current fromthe direct current source, said single thyristors normally conductingcurrent generated by the motor during the interval between pulses; ande. switching means for selectively supplying gate signals to each ofsaid respective pairs of thyristors and said single thyristor, saidswitching means serving to supply gate signals to said single thyristoronly when gate signals are supplied to one of said pairs of thyristors.